- about 300 CFM max - can be speed controlled about all the way to 0. - doesn't make a hum or whatever when speed controlled. - Absolutely as quiet as possible.
I've heard that if you compare a small fan with a large fan that's turned down with a speed control to move the same CFM as the small fan, the large fan will be quieter.
Somebody at Fantech told me this wasn't true, that the noise just depends on the CFM the fan is moving. I don't believe this (she said other very dubious things), because I've heard elsewhere that a larger fan will be moving with a lower RPM when it's moving the same amount of air, so it would be quieter.
So, I figure I'd get about a 300 CFM fan and turn it down with a speed control. My range is very small and it doesn't need a big fan.
Some fans make a low-voltage hum when you use a speed control on them. Fantech said their fans do. Someone at Broan told me their inline duct fan doesn't have a low-voltage hum when speed controlled. I don't know how big of a deal the low-voltage hum is, compared to the noise from the fan motor.
What inline fans are quietest? They don't have a standard way of testing the noise from them, unfortunately.
I know stuff about reducing the noise that's moving through the duct - duct silencer, liquid soundproofing you can spray inside the duct. Etc. etc. My question though is about the quietest *fan*.